1. Field of the Invention
The present invention generally relates control of a plurality of storage devices attached to a server system. More particularly, the present invention relates to a method for controlling a plurality of storage devices connected to a host server system from a network server system.
2. Description of the Related Art
Computers and their application programs are used in all aspects of business, industry and academic endeavors. In recent years, computer systems having a server system and/or other networked server systems have become prevalent, and many types of server systems have been developed. In one type of server systems, a plurality of network server systems are connected to a host server system. The host server system includes an IOP (Input/Output Processor) having a SCSI (Small Computer System Interface) bus/port and a plurality of SCSI devices are attached to the SCSI bus/port. The SCSI devices may include a plurality of storage devices, such as a DASD (Direct Access Storage Device), an optical storage device, and a tape drive.
When access and control of a particular SCSI device from the network server systems are desired, the network server operating system generates a device request for the particular SCSI device. The device request calls a device drivers from a library of device drivers available on the network server operating system, and the device driver for the particular SCSI device creates a host server system request for the command to the particular SCSI device attached to the host server system. The device driver sends the host server system request to an IOP of the network server system, which communicates with the IOP of the host server system. The host server system request is received and processed by the IOP on the host server system, and the requested task is performed on the particular SCSI device attached to the host server system.
Since the processor chip on the IOP of the network server system typically has only one or two interfaces for communicating with the plurality of device drivers, synchronization mechanisms designed for synchronizing the plurality of device drivers on the network server system are require for the IOP on the network server system to perform properly. However, the synchronization mechanisms degrade performance of the IOP on the network server system and increase complications to the codes for the plurality of device drivers.
Therefore, there exists a need for a method for controlling a plurality of storage devices connected to a host server system from a network server system which does not require synchronization of a plurality of device drivers on the network server system. It would be desirable for the method to provide improved performance of the network server system and simplification of codes for the device driver.